Vietnam Journal of Mechanics

Application of newly proposed hardening laws for structural steel rods

Van Nam Nguyen — 2024-06-04

In civil engineering, distinct mechanical properties and behaviors of structural steel rods necessitate a novel approach to material modeling. This study extends the application of recently proposed strain-hardening laws, originally developed for automotive sheet metals, to several structural steel rods (CB240-T and CB300-T). Standard uniaxial tensile tests are conducted for each examined material to obtain experimental stress-strain data. Various curve fitting methods are then employed to refine the parameters of the strain-hardening laws, enabling accurate representation of the steel rods mechanical behavior. Subsequently, these laws are implemented in Abaqus software for numerical simulation of uniaxial tensile tests, facilitating the analyses of material response under uniaxial tensile loading condition. Compared to the measured data, the predicted force-displacement curves are in good agreement with the measurements until the tail of the curves. The comparisons verify the ability and potential of the examined hardening law for studying the post-necking behavior of structural steels. The outcomes provide a framework for more precise characterization of structural steel materials.

Wave propagation in context of Moore–Gibson–Thompson thermoelasticity with Klein–Gordon nonlocality

Baljeet Singh — 2024-06-10

Understanding plane and surface waves in elastic materials is crucial in various fields, including geophysics, seismology, and materials science, as they provide valuable information about the properties of the materials they travel through and can help in earthquake detection and analysis. In the present paper, the governing equations of Moore–Gibson–Thompson (MGT) thermoelasticity are modified in context of Klein–Gordon (KG) nonlocality. For linear, homogeneous and isotropic case, the governing equations in two-dimensions are solved to obtain the dispersion relations for possible plane waves. It is found that there exists one transverse and two coupled longitudinal waves in a two-dimensional model of MGT weakly nonlocal thermoelastic medium and the speeds of these plane waves are found to be dependent on KG nonlocal parameters. The coupled longitudinal waves are also found to be dependent on conductivity rate parameter. For linear, homogeneous and isotropic case, the governing equations in two-dimensions are also solved to obtain a Rayleigh wave secular equation at thermally insulated surface. For a numerical example of aluminium material, the speeds of transverse wave, coupled longitudinal waves and the Rayleigh wave are computed and graphically illustrated to visualize the effects of KG nonlocality parameters, conductivity rate parameter and the angular frequency on the wave speeds.

Size-dependent nonlinear bending of microbeams based on a third-order shear deformation theory

Ngoc Duyen Dang — 2024-06-10

In this paper, the size-dependent nonlinear bending of microbeams subjected to mechanical loading is studied using a finite element formulation. Based on the von Kármán nonlinear relationship and the third-order shear deformation theory, a size-dependent nonlinear beam element is derived by using the modified couple stress theory (MCST) to capture the microstructural size effect. The element with explicit expressions for the element vector of internal forces and tangent stiffness matrix is derived by employing the transverse shear rotation as a variable. Nonlinear bending of microbeams under different mechanical loading is predicted with the aid of Newton–Raphson iterative method. Numerical investigation shows that the derived element is efficient, and it is capable of giving accurate results by several elements. The obtained results reveal the importance of the micro-size effect on the nonlinear behavior of the microbeams, and the deflections are overestimated when the microstructural effect is ignored. The effects of the material length scale parameter, boundary conditions and loading type on the bending response of the microbeams are studied and highlighted.

Application of small punch test to estimate mechanical behaviour of SUS304 austenitic stainless steel

The Yen Doan — 2024-06-11

The small punch test with an application of a relatively small specimen has recently become a reliable material mechanics testing method. In this study, the small punch test is set up based on the conventional mechanical testing machine for SUS304 stainless steel to evaluate the mechanical properties of SUS304 steel at different displacement rates of the punch in quasi-static loading condition in the case of with and without heat treatment. Although heat treatment has an insignificant effect on the microstructure and hardness of the material, the mechanical properties of the material in the small punch test are greatly reduced after heat treatment. Both cases with and without heat treatment have a similar tendency for the rate - sensitivity of the applied force - displacement curve. A higher value of force is applied to obtain the same value of displacement at a low displacement rate in the stable plastic deformation zone. Meanwhile, the maximum value of applied force is higher at a higher displacement rate in the stage that initiation of crack might appear. In the examined range of displacement rate, a positive rate - sensitivity of displacement at the maximum force. Therefore, a correlation between equivalent fracture strain and fracture toughness of the material can be achieved.

Three versions of Galerkin's method applied to the static deflection of a stepped beam

Joel Storch — 2024-06-29

This work deals with the application of Galerkin's method for stepped structures to evaluate the static deflection under distributed loading. In this study, we compare two different implementations of the well-known method to the exact analytical result in order to prove that only the second method is able to give a good approximation to the solution of the problem.

Integration of Genetic Algorithm and Hedge Algebras in controlling mechanical machining robots

Phan Bui Khoi — 2024-06-29

Robot applications in mechanical processing have become popular. The critical issue when applying robots in mechanical processing is ensuring accuracy. Usually, robot control is based on dynamic models. This method has difficulty accurately determining the system's dynamic model because the robot has a complex structure. Besides, dynamic factors such as cutting force, friction force and machining conditions constantly change. Robot control based on Hedge Algebras gives excellent and reliable results. The critical factors that determine the quality and reliability of the Hedge Algebra controller are the Control Law, the method of Denormalization, and the determination of the Physical Value Domain. The construction of the Control Law and Denormalization is based on expert knowledge. Determining the physical value domain is problematic because it requires many experiments. This article introduces the method of applying genetic algorithms to find the appropriate physical value domain for the controller based on Hedge Algebras. The article presents a robot controller based on Hedge Algebras to do this. Numerical experiments with a mechanical machining robot verify the results.

An analytical nonlinear displacement model of electrothermal V-shaped actuator

Kien Trung Hoang — 2024-06-29

This work presents an analytical model to determine nonlinear displacements of electrothermal V-shaped actuators. The nonlinear displacement model of V-shaped beams fixed at both ends is established based on considering the axial deformation of the beam. The 3D model of the V-shaped microactuator was established to verify the theoretical nonlinear model. The evaluation shows that the displacement deviation between the analytical nonlinear model and simulation is approximately 7.7% at the driving voltage of 16 V. This confirms the advantages of the proposed model to predict more precisely the displacement of the electrothermal V-shaped actuator.